1. Field of the Invention
The invention generally relates to a method and an apparatus for manufacturing a cylindrical member by flow forming, and a cylindrical member having inner splines that is manufactured by using the method and the apparatus. More particularly, the invention relates to a method and an apparatus for partially thickening a blank, and a product manufactured by using the method and the apparatus, which are preferably applied to a front cover of a torque converter having inner splines.
2. Description of Related Art
Conventionally, some parts of the automatic transmission have splines formed at radially inward positions. For example, Japanese Laid-Open Publication No. 9-317848 describes a front cover of a torque converter. This front cover has inner splines for engaging the components such as outer friction plates in a lockup clutch composed of a multiple disc clutch. In this front cover, a drum member having the splines formed at its inner peripheral surface are welded within the front cover of sheet metal.
A cylindrical member having such splines, e.g., a front cover, is constructed by integrally welding a main body and another member having the splines. This requires troublesome processes such as welding, and also requires advanced production management such as preventing a residual sputtering material from being left within the product. Moreover, the number of parts is increased, resulting in increased costs.
For example, U.S. Pat. No. 5,718,311 describes a method for integrally forming a front cover portion and spline grooves by flow forming. However, in such a simple flow forming method, the thickness of the splined portion is significantly reduced. In view of the strength, a countermeasure is required such as forming the entire structure from a thick blank. Forming not only the splined portion but also the entire structure with a large thickness causes additional problems like increased weight of the torque converter.
In order to solve the above problems, the applicant proposed a method for manufacturing a cylindrical member having splines in Japanese Laid-Open Publication No. 11-266062. According to this method, as shown in FIG. 12(a), a disk-shaped blank 1 is fixedly held between a tailstock 2 and a mandrel 3. A multiplicity of tooth spaces 3a corresponding to the splines are formed at the outer peripheral surface of the mandrel 3. These tooth spaces 3a may either extend in the central-axis (Z-axis) direction, or may be slightly tilted with respect to the central axis. As shown in FIG. 12(b), a thickening roller 5 having a dish-shaped outer peripheral surface 5a is rotated and moved in the direction A, thereby pressing the blank 1 from the outer peripheral end face. As a result, the thickness of the blank 1 is increased (from t1 to t2), and the blank 1 is bent toward the mandrel 3. As shown in FIG. 12(c), a forming roller 6 is then rotated and moved in the direction B (Z-axis direction). As a result, the portion 1a thickened by the thickening roller 5 is spread along the mandrel 3 by plastic deformation, whereby the thickness thereof is reduced (from t2 to t3). The material thus spread is forced into the grooves 3a, whereby the splines 1b are formed.
According to the flow forming proposed by the applicant, only the portion of the front cover (cylindrical member) 1 corresponding to the splines 1b is thickened, and the front cover need not entirely be thickened, enabling reduction in weight of the torque converter. However, the blank to be formed into the cylindrical portion is entirely pressed to form the thick portion (see FIG. 12(b)), causing work hardening. Therefore, the material does not sufficiently flow into the space between the teeth 3a of the mandrel 3 in the subsequent step of forming the splines 1b with a roller 6. Accordingly, the accuracy of the splines may possibly be degraded. This problem becomes remarkable in forming the cylindrical member having a longer cylindrical portion. Moreover, the forming roller 6 is moved in the direction B. Therefore, the roller 6 pulls a shoulder portion 1e at the boundary between a circular plate portion 1c and a cylindrical portion 1d. As a result, a sufficient amount of material is less likely to remain in the shoulder portion, although the shoulder portion is subjected to large stresses for the structural reason.
Moreover, this flow forming requires large processing energy in order to thicken the entire columnar portion of the blank 1. In the case where the blank 1 as punched with a press is directly used, the accuracy of the outer peripheral end face 1f is not enough. When pressed against the outer peripheral end face of the blank, the thickening roller 5 is subjected to the large loads, and therefore the outer periphery of the thickening roller 5 is damaged by the rough end face 1f of the blank, resulting in relatively short lifetime of the roller. However, finishing the outer peripheral end face of the blank with high accuracy would require additional processes such as cutting process.
The applicant also proposed a driving apparatus for hybrid vehicles in which an electric motor 11 is mounted radially outside the torque converter 10 as shown in FIG. 13 (e.g., Japanese Patent Application No. 11-84924 and Japanese Patent Application 11-104540, which had not been laid-open upon filing of the present application). As shown in FIG. 13, a front cover 12 of a torque converter 10 has a stepped structure having an axially extending flat portion 12a in a radially intermediate portion. The front cover 12 also has a vertical portion (bottom) 12b located radially inside the flat portion. An enlarged diameter portion 12c is formed radially outside the flat portion 13 in order to accommodate a turbine runner 13. An electric motor 11 composed of a rotor 11a and a stator 11b is mounted radially outside the flat portion 12a with a predetermined space c interposed between the rotor and the flat portion 12a. The lockup clutch 15 is mounted radially inside the flat portion 12a. 
The lockup clutch 15 is composed of a multiple disc clutch having a multiplicity of external friction plates (drive plates and backup plates) 16 and inner friction plates (driven plates) 17. The drum member 19 has its one end welded to the front cover 12 and extends along the flat portion 12a. Inner splines 19a are formed in the drum member 19. The outer friction plates 16 are engaged with the inner splines 19a. The inner friction plates 17 are engaged with hubs 23 connected to an input shaft 22 of a transmission 21 (automatic transmission (A/T) or continuously variable transmission (CVT)) through a damper spring 20.
The lockup clutch 15 is connected with a hydraulic pressure of a piston 26 driven with a hydraulic pressure supplied to an oil chamber 25. The torque capacity of the lockup clutch 15 is determined by the lining area of the friction members 16, 17. As described above, however, the outer friction plates 16 are engaged with the splines 19a formed in the drum member 19. Therefore, the friction members are located radially inward as compared to the case where the splines are directly formed in the front cover 12. Moreover, the length thereof is also reduced. Accordingly, a sufficient lining area of the friction members cannot be ensured, and therefore sufficient torque capacity of the lockup clutch cannot be ensured with respect to the maximum required design hydraulic value.
In this lockup clutch 15, the outer friction plates 16 are engaged with the drum member 19 that is a member separate from the front cover 12. As described above, from the manufacturing and functional point of view, it is desirable to eliminate the drum member and form the inner splines 19a in the front cover itself. However, in the case where an integral front cover 12 is formed by the aforementioned flow forming (see FIG. 12), the following problem will occur: as shown in FIG. 14, when the blank 1 is pressed with the thickening roller 5, the outer peripheral end face 1f of the blank 1 abuts on the increased diameter portion 3c of the mandrel 3 corresponding to the enlarged diameter portion 12, thereby excessively increasing the processing loads. In this case, it is difficult to thicken the portion 1g corresponding to the tooth spaces 3a of the mandrel 3. Therefore, the tooth spaces 3a cannot be sufficiently filled with the material.
Accordingly, it is an object of the invention to provide a method and an apparatus for manufacturing a cylindrical member by flow forming which solve the above problem by partially thickening a blank, and a cylindrical member having splines that is formed by using the method and the apparatus.
In order to achieve the aforementioned object, in a first aspect of the invention, a method for manufacturing a cylindrical member from a blank includes a step of partially thickening the blank by moving, on the blank held by a mandrel, a thickening roller in a radially inward direction from an intermediate portion of the blank while pressing the thickening roller against the blank, the intermediate portion being located radially inside an outer peripheral end face of the blank.
Therefore, only a required portion of the blank can be thickened by a required amount. This reduces the damage to the material, and also reduces work hardening, whereby the cylindrical member can be manufactured accurately with reduced processing loads and reduced processing energy.
Moreover, the thickening roller abuts on the blank from the intermediate portion thereof. Accordingly, even if a shear surface or a rupture surface is directly used as the outer peripheral end face of the blank, the thickening roller will not be damaged. This, together with the reduced processing loads, can improve the lifetime of the thickening roller. Moreover, the blank can be directly used as punched. This eliminates the need for the processes such as cutting, allowing improvement in manufacturing efficiency.
In a preferred form of the first aspect of the invention, the mandrel includes a columnar portion extending approximately in parallel with an axial direction, and an increased diameter portion having a larger diameter than that of the columnar portion. The blank is bent such that an radially outward surface of the blank abuts on the increased diameter portion, and the thickening step using the thickening roller is conducted with the radially outward surface being supported on the increased diameter portion.
Therefore, the blank is subjected to the thickening step with the side surface thereof being supported on the increased diameter portion of the mandrel. Accordingly, with the thickening roller, the material is reliably plastic deformed and flows, ensuring sufficient thickening of the blank.
In another preferred form of the first aspect of the invention, tooth spaces for splining are formed in the columnar portion of the mandrel, and the cylindrical member having inner splines is formed by pressing the portion thickened by the thickening step into the tooth spaces.
Therefore, the material at the thickened portion is pressed into the tooth spaces in the columnar portion of the mandrel, whereby the splines can be formed in the thickened portion.
In still another preferred form of the first aspect of the invention, the method further includes a step of forming the blank by moving a forming roller relatively in the axial direction of the mandrel while pressing the blank. The forming step is conducted after the thickening step.
Therefore, a cylindrical member having a thickened portion, and in particular, having splines at the thickened portion, can be reliably produced with the forming roller, according to the shape of the mandrel.
In yet another preferred form of the first aspect of the invention, the mandrel is formed by integrally combining the columnar portion and the increased diameter portion, and the forming roller is moved along the columnar portion and the increased diameter portion so as to form the cylindrical member having a flat portion corresponding to the columnar portion and an enlarged diameter portion corresponding to the increased diameter portion.
Therefore, the use of such a mandrel integrally comprising the cylindrical portion and the increased diameter portion facilitates accurate formation of a cylindrical member (e.g., a front cover of FIG. 13) having an enlarged diameter portion, which is conventionally difficult with flow forming.
In a further preferred form of the first aspect of the invention, the mandrel includes a main body having the columnar portion, and a movable portion movable in the axial direction relative to the main body and having the increased diameter portion. In the thickening step, the movable portion is held at such a position that the blank abuts on the increased diameter portion, and in the forming step, the movable portion is moved to such a position that the blank does not abut on the movable portion, whereby the cylindrical member corresponding to the main body is formed.
Therefore, the use of the mandrel having a movable portion allows manufacturing of not only a cylindrical member having an enlarged diameter portion but also a cylindrical member having no enlarged diameter portion (stepped portion).
In a still further preferred form of the first aspect of the invention, the method further includes a step of pressing the portion thickened by the thickening step against the columnar portion of the mandrel by moving a pressing roller in a radially inward direction. The pressing step is conducted between the thickening step and the forming step.
Therefore, the thickened portion is pressed against the columnar portion of the mandrel by using the pressing roller. This allows improvement in accuracy of the flat portion corresponding to the columnar portion, in particular, the flat portion with splines.
In a yet further preferred form of the first aspect of the invention, the thickening roller has an outer peripheral surface tilted by a predetermined angle such that, in the columnar portion, a material flows in a radially inward direction of the blank.
Therefore, the thickening roller has a tilted outer peripheral surface. This prevents an underfill portion from being produced at the joint between the bottom and the flat portion of the cylindrical member, that is, at the shoulder portion that is subjected to large stresses for the structural reason. Accordingly, a strong cylindrical member can be reliably manufactured.
In a second aspect of the invention, an apparatus for manufacturing a cylindrical member from a blank includes: a mandrel; a fixing member for holding the blank against the mandrel; and a thickening roller moving in axial and radial directions relative to the mandrel. The blank is partially thickened by moving, on the blank held by the mandrel and the fixing member, the thickening roller in a radially inward direction from an intermediate portion of the blank while pressing the thickening roller against the blank, the intermediate portion being located radially inside an outer peripheral end face of the blank.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the first aspect of the invention can be obtained.
In a preferred form of the second aspect of the invention, the mandrel includes a columnar portion extending approximately in parallel with the axial direction, and an increased diameter portion having a larger diameter than that of the columnar portion. The blank is bent such that an radially outward side surface of the blank abuts on the increased diameter portion, and the thickening roller is operated so as to partially thicken the blank with the radially outward side surface being supported on the increased diameter portion.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the preferred aspect of the preferred form of the first aspect of the invention can be obtained.
In another preferred form of the second aspect of the invention, tooth spaces for splining are formed in the columnar portion of the mandrel, and the cylindrical member having inner splines is formed by pressing the portion thickened by the thickening step into the tooth spaces.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the another preferred form of the first aspect of the invention can be obtained.
In still another preferred form of the second aspect of the invention, the apparatus further includes a forming roller operated so as to move relatively in the axial direction of the mandrel while pressing the blank.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the still another preferred form of the first aspect of the invention can be obtained.
In yet another preferred form of the second aspect of the invention, the mandrel is formed by integrally combining the columnar portion and the increased diameter portion. The forming roller is moved along the columnar portion and the increased diameter portion so as to form the cylindrical member having a flat portion corresponding to the columnar portion and an enlarged diameter portion corresponding to the increased diameter portion.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the yet another preferred form of the first aspect of the invention can be obtained.
In a further preferred form of the second aspect of the invention, the mandrel includes a main body having the columnar portion, and a movable portion movable in the axial direction relative to the main body and having the increased diameter portion. During operation of the thickening roller, the movable portion is held at such a position that the blank abuts on the increased diameter portion, and during operation of the forming roller, the movable portion is moved to such a position that the blank does not abut on the movable portion, whereby the cylindrical member corresponding to the main body is formed.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the further preferred form of the first aspect of the invention can be obtained.
In a still further preferred form of the second aspect of the invention, the apparatus further includes a pressing roller operated so as to press the portion thickened by the thickening roller against the columnar portion of the mandrel.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the still further preferred form of the first aspect of the invention can be obtained.
In a yet further preferred form of the second aspect of the invention, the thickening roller has an outer peripheral surface tilted by a predetermined angle such that a diameter of the thickening roller is reduced toward a portion of the blank that is held by the mandrel and the fixing member.
Therefore, a manufacturing apparatus capable of reliably achieving the effects described in the yet further preferred form of the first aspect of the invention can be obtained.
In a yet further preferred form of the second aspect of the invention, the mandrel and the fixing member are rotatable and movable in an axial direction, and the thickening roller and the forming roller are movable in an axial direction relative to the mandrel.
Therefore, the mandrel is movable in the axial direction, and the thickening roller and the forming roller are movable in the radial direction. With such a simple structure, cylindrical members having various shapes corresponding to the mandrel can be easily manufactured in a reliable manner by controlling the timing and speed of the movement of the combination of these elements.
In a yet further preferred form of the second aspect of the invention, the apparatus further includes a turret rotatable about an axis extending in parallel with the axis of the mandrel. The thickening roller and the forming roller are supported on the turret, and by rotating the turret, the thickening roller or the forming roller is moved so as to face the mandrel.
Therefore, the thickening roller and the forming roller are supported on the turret so that the rollers sequentially face the mandrel as required. Accordingly, the cylindrical member can be efficiently manufactured in an automated manner.
In a yet further preferred form of the second aspect of the invention, the forming roller is composed of a plurality of different types of rollers such as a rough roller and a finishing roller.
Therefore, the cylindrical member can be formed with improved accuracy by using the forming roller composed of the plurality of different types of rollers.
In a third aspect of the invention, a cylindrical member manufactured from a blank integrally comprises: a bottom having a thickness approximately the same as that of the blank; a flat portion extending approximately in parallel with an axial direction, and including a thick portion having a thickness larger than that of the blank; and inner splines formed at an inner peripheral surface of the thick portion.
Therefore, the cylindrical member includes the bottom having a thickness approximately the same as that of the blank and the flat portion including a thick portion having a thickness larger than that of the bottom. Moreover, the inner splines are integrally formed at the inner peripheral surface of the thick portion. Therefore, a sufficiently strong, splined cylindrical member having a predetermined thick portion as a spline portion can be obtained without increasing the total weight of the cylindrical member.
In a preferred form of the third aspect of the invention, the bottom is integrally connected to one axial end of the flat portion, and an enlarged diameter portion having a larger diameter than that of the flat portion is integrally connected to the other axial end of the flat portion.
Therefore, a cylindrical member having an enlarged diameter portion integrally connected to the other axial end of the flat portion and also having splines integrally formed in the thick portion can be obtained.
In another preferred form of the third aspect of the invention, the cylindrical member is a front cover of a torque converter.
Therefore, the torque converter including a flat portion and an enlarged diameter portion has the splines directly formed at the inner peripheral surface of the flat portion. Therefore, outer friction members having a large diameter is engaged with the splines, whereby the torque capacity of the friction members can be assured.
In still another preferred form of the third aspect of the invention, outer friction members of a lockup clutch composed of a multiple disc clutch is engaged with the splines formed at the inner peripheral surface of the flat portion. An electric motor is provided radially outside the flat portion.
Therefore, in the case where the outer diameter of the electric motor is specified in view of the in-vehicle dimensional limit, the electric motor can be mounted radially outside the flat portion of the front cover in order to satisfy such dimensional requirement. Moreover, the lining area is increased by forming the splines directly in the front cover. Therefore, required torque capacity of the lockup clutch located radially inside the flat portion can be assured.
In a fourth aspect of the invention, in a method for manufacturing a cylindrical member from a blank by using a mandrel, the mandrel includes a columnar portion and an increased diameter portion having a larger diameter than that of the columnar portion, and the columnar portion extends approximately in parallel with an axial direction and has tooth spaces for splining formed at its outer peripheral surface. The method includes a step of: accumulating a material at an enlarged diameter portion of an intermediate portion of the blank on a flat portion of the intermediate portion by moving, on the blank held by the mandril, a thickening roller along the increased diameter portion toward the columnar portion while pressing the intermediate portion of the blank against the increased diameter portion of the mandrel. The intermediate portion is located radially inside an outer peripheral end face of the blank, the enlarged diameter portion corresponds to the increased diameter portion of the mandrel, and the flat portion corresponds to the columnar portion of the mandrel. In the thickening step, a void having no material filled therein is provided at an intersection of the increased diameter portion and the columnar portion of the mandrel so that an underfill portion corresponding to the void is provided at a corner of the blank where the enlarged diameter portion and the flat portion intersect each other.
Therefore, in the step subsequent to the thickening step such as the pressing step or the forming step, the material in the flat portion smoothly flows into the void and will not flow back toward the shoulder portion. Accordingly, the bottom can be prevented from being curved (deformed) near the shoulder portion.
In a preferred form of the fourth aspect of the invention, the method further includes a step of pressing, in an axially inward direction, an outer peripheral surface of the flat portion thickened by the thickening step by using a pressing roller, so as to force the material at an inner peripheral surface of the flat portion into the tooth spaces. The pressing step is conducted after the thickening step.
Therefore, the material at the inner peripheral surface of the flat portion is pressed into the tooth spaces in the pressing step. At this point, the material in the flat portion smoothly flows into the void and will not flow back toward the shoulder portion. Accordingly, the bottom can be prevented from being curved (deformed) near the shoulder portion.
In another preferred form of the fourth aspect of the invention, the tooth spaces and the void are filled with the material in the pressing step.
Therefore, manufacturing of the cylinder member can be completed by filling the tooth spaces and the void with the material in the pressing step. At this point, the material in the flat portion smoothly flows into the void and will not flow back toward the shoulder portion. Accordingly, the bottom can be prevented from being curved (deformed) near the shoulder portion.
In still another form of the fourth aspect of the invention, a portion that is not filled with the material is left in the tooth spaces and the void in the pressing step.
Therefore, the material at the inner peripheral surface of the flat portion is pressed into the tooth spaces in the pressing step. At this point, a portion that is not filled with the material is left in the tooth spaces and the void. Therefore, backflow of the material can be prevented, for example, in the case where the forming step is conducted after the pressing step.
In yet another form of the fourth aspect of the invention, the method further includes a step of forming the blank by moving a forming roller in the axial direction toward the corner while pressing an outer peripheral surface of the flat portion in a radially inward direction in order to fill the non-filled portion in the tooth spaces and the void with the material. The forming step is conducted after the pressing step.
Therefore, manufacturing of the cylinder member can be completed by filling the tooth spaces and the void with the material in the forming step subsequent to the pressing step. At this point, the material in the flat portion smoothly flows into the void and will not flow back toward the shoulder portion. Accordingly, the bottom can be prevented from being curved (deformed) near the shoulder portion.